How did the Roman aristocracy treat/view plebeians? Were they treated differently at different points in the republic?

Much of the historical narrative that we have for the early Republic is dominated by the so-called struggle of the orders. This was sort of a civil rights campaign by the plebeians for equal rights. At this stage the patricians were a handful of established aristocratic families, and the plebeians were everyone else. At first, the patricians monopolised all the major political and religious offices, but the plebeians gradually won the right to hold these positions. One of the most important victories for the plebeian cause came in 367 BC, when a law was passed guaranteeing at least one plebeian consul; subsequently more and more offices were opened up to plebeians. (It should be noted that the literary sources we have for this period are much later, and are therefore open to question. But we don't have anything better to go on, so most historians tend to assume that the surviving narratives are based on a factual core even if many of the details are invented or distorted.)

By the late Republic, the patrician-plebeian distinction was largely redundant. There were still patrician families, but these were not synonymous with the office-holding nobility, as they had once been. Being a patrician could even be seen as a disadvantage: one patrician, the populist politician Publius Claudius Pulcher (wow, alliteration), had to be adopted into a plebeian family in order to stand for the office of tribune (he became Publius Clodius Pulcher in 59 BC as a result). In late Republican parlance, "plebs" became a more general term to refer to the common people, meaning anyone who didn't belong to the senatorial or equestrian classes, except in technical cases like that of Clodius.